The present invention relates to test strips useful for detecting components in a test sample, and particularly to stable test strips comprising a reagent layer containing a dialyzed polymer. Typically, the test strip is used to test for the presence of a specific substance such as sugar in a liquid.
The analysis of test samples by use of test strips find utility in a variety of areas ranging from the medical field to food industries. Depending upon the reagent(s) present in the test strip, the strip can be used in detecting and diagnosing a variety of different conditions ranging, for example, from diabetes to pregnancy. In the food industry, the presence of, for example, maltose can be monitored in brewing where starch is converted to sugars such as maltose prior to fermentation to assure high yield from the grain starting materials.
Typically, test strips take advantage of a reaction between the substance to be tested and a reagent system present in the test strip. Generally, the test strip will take advantage of a color change or change in the wave length absorbed or reflected by the reagent system used as a result of this reaction. See, U.S. Pat. No. 3,802,842, U.S. Pat. No. 4,061,468 and U.S. Pat. No. 4,490,465. In testing for the presence of a substance such as sugar in a bodily fluid, test strips commonly take advantage of an oxidation/reduction reaction which occurs. The test strip is exposed to a drop of the fluid to be tested for a suitable period of time and there will be a color change if the sugar is present. Typically, the intensity of this change is proportional to the concentration of the sugar in the sample. The color of the test strip is than compared to a known standard which enables one to determine the amount of sugar present in the sample. This determination can be made by a visual check or by an instrument, such as using a light absorption or light transmission spectrophotometer for more accurate evaluation of concentration in the sample.
Because of the diagnostic applications, it is very important that the results obtained by these tests are reliable. Preferably, these strips will also have a long shelf life. One method for determining reliability and shelf life is by use of accelerated aging which comprises incubating the strip at an elevated temperature, e.g. 60.degree. C., for a number of hours. We have now found that by constructing the strip by using a dialyzed latex polymer in the reagent layer, the resulting test strip maintains its integrity for a substantially longer time when exposed to elevated temperatures than a strip constructed using undialyzed polymer. Such elevated temperatures can be encountered during shipping or when stored in uncontrolled environments such as, for instance, the glove compartment of a car.